Chromosomal abnormalities..

I finished Peter Jensen’s book, which I also mentioned in the previous post, this morning, and I decided to add a few comments and links to articles covering stuff he also covers in his book. I liked the book and gave it 3 stars on goodreads. It’s old – from 1998 – so a lot of stuff has happened since then in this field (e.g. ‘new’ genetic diseases, such as 17q21.31 microdeletion syndrome, have been ‘discovered’ – though I should caution here that according to Jensen a distinction is to be made between ‘chromosomal abnormalities’ and ‘genetic diseases’; unlike many genetic disorders, chromosomal abnormalities involve mutations which are large enough to be seen using an ordinary light microscope). However my working assumption has been that most of the stuff covered in the book is unlikely to have changed much; how a chromosomal abnormality affects the individuals who have it doesn’t change much from one decade to another, even though improvements in medical technology may have improved outcomes for some specific diseases.

Some links to stuff he talks about in the book, in no specific order: Chromosome abnormality (I should add that pretty much every link in that article is to an article on something which is also covered in the book), Aneuploidy, Robertsonian translocation, Klinefelter syndrome, Turner Syndrome, Williams Syndrome, Down Syndrome, Patau syndrome, Fragile X syndrome, Angelman Syndrome, Prader-Willi syndrome, Barr body, Non-disjunction, Amniocentesis, Trisomy 8, FMR1.

A few general remarks: It should be noted that autosomal chromosomal abnormalities are usually more severe than sex-linked chromosomal abnormalities. More than 95% of chromosomal abnormalities result in spontaneous abortion, and 60% of early spontaneous abortions (within the first trimester) are due to chromosomal abnormalities. Monosomies (including partial ones) tend to have more severe consequences than do trisomies. Even though people tend to think that way about genetic diseases not all chromosomal abnormalities are best thought of as inhabiting a binary event space (either you have it or you don’t); some of them display to a significant extent a dose–response relationship (see e.g. the articles on the FMR1 gene & Fragile X syndrome). As should be obvious from the number of associated abortions, many of the chromosomal abnormalities (particularly the autosomal ones) lead to really horrible outcomes: Among Pataus Syndrome sufferers less than 40% survive past [remember: 1998 numbers] one week after birth, and only 4,5% survive past 6 months [according to wikipedia’s article on the topic, “More than 80% of children with Patau syndrome die within the first year of life” – so mortality is still very high]; when it comes to Edward’s syndrome likewise approximately 60% died within a week, and around 5% were still alive after a year back then – and this is just considering the variable survival, not stuff like blindness, polydactyli, organ malformation (brain, heart, kidneys, …), deafness, etc., etc., which are also very often present in people with these disorders…

Incidentally I read most of Carpe Jugulum today, but I won’t blog that one until tomorrow.


June 7, 2013 - Posted by | Books, Genetics, Medicine

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